Proton therapy uses a beam of protons to irradiate diseased tissue, most often in the treatment of cancer. The chief advantage of proton therapy is the ability to more precisely localize the radiation dosage when compared with other types of external beam radiotherapy.
During treatment, a particle accelerator is used to target the diseased tissue with a beam of protons. Due to their relatively large mass, protons have little lateral side scatter in the tissue. The beam does not broaden much, stays focused on the shape of the diseased tissue and delivers low-dose side-effects to surrounding tissue. All protons of a given energy have a certain range, with very few protons penetrating beyond this range. The dose delivered to the tissue is maximum just over the last few millimeters of the particle's range, which is called the Bragg peak.
A radiation aperture body (i.e., aperture) and a radiation filter (i.e., a range compensator) are beam modifying devices that control the shape and penetration of protons during treatment of a patient. These devices are typically connected to an output of a radiation source of a radiation therapy apparatus. The radiation aperture body is typically brass and can be up to several inches thick, and has a shaped opening therein to control the radiation dosing profile. The radiation filter is three-dimensionally shaped to direct the protons to the desired target area on the patient to ensure that the target receives the correct radiation dose, while the healthy tissue surrounding the target receives substantially less radiation. Careful registration or indexing of the radiation filter and the radiation aperture body ensures that the patient has the proper exposure in the target area, such that the proton's energy is released within the target area.
A typical radiation therapy apparatus does not fully expose the radiation aperture body to the protons. Consequently, there is a border region around the perimeter of the radiation aperture body which is not exposed to the protons. As noted above, the radiation aperture body is typically brass and can be up to several inches thick. Brass is a fairly expensive material compared to other high density materials, and the excess brass in the border region adds to the cost of the radiation aperture body.
One approach to reduce the cost of the radiation aperture body is to replace a portion of the brass border region with a non-brass frame that carries the radiation aperture body, as disclosed in U.S. published patent application no. 2011/0127443. The frame and the radiation aperture body are dimensioned so that the radiation aperture body is still not fully exposed to the protons, but since the volume of the radiation aperture body is reduced, less brass is needed resulting in a cost savings. Nonetheless, there is still a need to further reduce the cost of a radiation aperture body.